VSV infects a wide variety of animal cells and has been used as a prototype for studying the mechanism of replication and assembly of enveloped viruses. Recently, there has been renewed interest in the study of virus uptake into host cells. Such studies have not only elucidated basic characteristics of cell function but have also given focus to new antiviral therapies. Our laboratory has been investigating the internalization of VSV into host cells in an attempt to (1) define the plasma membrane binding site for VSV, (2) determine the specificity characteristics o this binding, (3) dissect the mechanisms by which VSV fuses with cell membranes, and (4) explore possible mechanisms for inhibiting or perturbing the early steps of infection. We will use multiple approaches to study the internalization of VSV. Binding assays with purified S35-VSV will permit the detection of specific VSV binding. In addition, IF and EM techniques will be used to monitor the morphologic pathway of VSV entry. To analyze the fusion of virus and cell membranes, we will utilize liposomes containing VSV G protein (virosomes). These virosomes will be studied for their specificity of interaction with host cells and then used to study their interaction with other liposomes. Energy transfer fluorescence, fluorescence quenching, and EM will be used to quantitate and monitor the fusion process mediated by G protein. In addition, attempts will be made with circular dichroism and infra-red spectroscopy to follow possible conformational changes in G protein which occur during the fusion event. Neutralizing antibodies will be used to confirm relevant changes in protein conformation.